抄録
This paper describes a search for superposed effects in Sq as revealed by data taken from the publications of Lerwick and Eskdalemuir observatories. The method uses histograms representing the frequency with which different values of H are recorded, after first removing the secular change. The histograms are used to form their associated characteristic functions (Fourier transforms) which are then factorized by locating their zeroes. When the zeroes are all plotted in a suitable representation, the presence of superposed effects should be manifested by the zeroes forming families of radial lines.
The samples of data taken from Lerwick were found to be too small to yield satisfactory results; those from Eskdalemuir were more successful, although only the data relating to the epoch of maximum solar activity provided quantitative results. On the basis of this analysis it seems that the quiet daily variations in the horizontal component at Eakdalemuir in winter consist of two components. The first is dominant only during sunlight and its amplitude depends on the solar zenith angle; the other component is definitely non-cyclic in character.
The investigation also provides a value for the ‘zero level’ of Sq, the value the field would have if the Sq current system, including its purely zonal part, was arrested. Depending on certain assumptions this zero level appears to lie about 12 or 17nT above the daily mean value of field on International Quiet Days.
